A playback stylus which is employed to recover information recorded in a capacitive information disc generally includes a dielectric support element. Often diamond is employed as the dielectric support element because of its long-wearing capabilities although other materials such as sapphire may also be employed. In order to obtain playback styli at lower cost, the dielectric suppport element may be mounted on a shank of a less costly material including a metal such as titanium.
Playback styli may be manufactured by employing a dielectric support element having a conical surface at one end. For example, Matsumoto in U.S. Pat. Nos. 4,164,755 and 4,165,560 discloses a pick-up stylus fabricated from a tapered diamond support element having a plurality of conical portions with a common axis. Two of the conical portions are separated by an electrode bearing surface. A record engaging surface is provided in the tip region substantially orthogonal to the electrode bearing surface. The support element includes a pair of converging flat surfaces in the tip region which are disposed such that the intersection of the converging flat surfaces with the record engaging surface defines the side edges of the record engaging surface. The intersection of the converging flat surfaces with a conical portion remote from the electrode bearing surface forms a prow.
In a copending application of Dholakia entitled, "Flip-Flop Grinding Method", Ser. No. 292,284, filed Aug. 12, 1981, a method for manufacturing a playback stylus with two faces having substantially the same area is disclosed.
Miller in a copending application, which is being filed concurrently, entitled, "Video Disc Stylus", Ser. No. 292,058, filed Aug. 12, 1981, discloses a capacitive information disc playback stylus in which two flats are lapped in a conical tip of a dielectric support element and a portion of the conical tip serves as the electrode bearing surface.
Dholakia in a copending application entitled, "Playback Stylus and its Manufacture," Ser. No. 292,057, filed Aug. 12, 1981, discloses a method of manufacturing a playback stylus from a conical tip in which an electrode bearing surface is lapped in the terminating portion of a conical tip.
In the aforementioned copending applications of Dholakia and Miller a signal recovering terminating portion which includes a record engaging surface is formed in the tip. One terminating signal recovering portion often employed is disclosed in Keizer, U.S. Pat. Nos. 4,104,832 and 4,162,510 in which a keel-tipped playback stylus and a method for forming the stylus are disclosed. The terminating portion of the tip is shaped to have a prow, a substantially flat rear surface remote from prow, a pair of substantially parallel side surfaces extending from the side edges of the rear surface, a bottom surface extending from the bottom edge of the rear surface, and additional surfaces extending from the prow intersecting the bottom and side surfaces.
I have found a problem in employing the conical tip dielectric support element bonded to a shank in preparing a capacitive information disc playback stylus. Generally a conical angle of 40 to 60 degrees is employed; a conical angle used in the audio stylus art. Attempts have been made to employ such audio styli in the manufacture of capacitive information disc playback styli. However, because of the increased amount of material that must be removed as a function of increasing conical angle when a signal recovering terminating portion such as a keel tip is prepared, a smaller conical angle, for example, 30 degrees, is preferred. However, the smaller conical angle results in a more fragile tip which readily breaks off. Also, attempts to prepare a stylus dielectric support element disc-engaging surface from this smaller conical angle results in a some of the shank portion being ground away. The shank material, such as titanium, poisons the abrasive lapping surface which results in a loss of abrasiveness with the concomitant need for longer lapping times and more frequent change of abrasive charge on the abrasive lapping surface. It would, therefore, be desirable to obtain a shanked dielectric support element having a small conical angle without the drawbacks I have observed.